Generally speaking, “global warming” refers to the observed increase in the average temperature of the Earth's atmosphere and oceans in recent decades and the projected continuation of this increase in tempratures. Models referenced by the Intergovernmental Panel on Climate Change (IPCC) predict that global temperatures are likely to increase by 1.1° to 6.4° C. (2.0° to 11.5° F.) between 1990 and 2100. The uncertainty in this range results from two factors, namely, differing future greenhouse gas (GHG) emission scenarios, and uncertainties regarding climate sensitivity.
Global average near-surface atmospheric temperature rose 0.74±0.18 degrees Celsius (1.3±0.32 degrees Fahrenheit) in the last century. The prevailing scientific opinion on climate change is that most of the observed increase in globally averaged temperatures since the mid-20th century is very likely to be due to the observed increase in anthropogenic greenhouse gas concentrations, leading to a warming of the Earth's surface and lower atmosphere by increasing the greenhouse effect. Greenhouse gases are released by activities such as the burning of fossil fuels, land clearing, agriculture, and the natural decay of trash in landfills.
Greenhouse gases are components of the atmosphere that contribute to the greenhouse effect. Some greenhouse gases occur naturally in the atmosphere, while others result from human activities. Naturally occurring greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Certain human activities, however, add to the levels of most of these naturally occurring gases. For example, decomposition of trash placed into a landfill is an anaerobic process that produces methane gas which, in turn, leaves the landfill as landfill gas. The amount of methane gas created from decomposition depends on a number of factors, but is generally proportional to the composition and amount of trash placed within the landfill. Thus, each ton of trash at a given composition that is placed into a landfill creates a predictable amount of methane gas. However, owners of landfills will often not take action to mitigate the greenhouse gases (such as methane gas) produced in a landfill because the costs of such mitigation are too high, and in many cases such mitigation actions are not required by the governmental regulating bodies which regulate landfill operations.
However, there is currently a global focus on reducing GHG emissions. In fact, both international and national initiatives are currently in force and others are pending or under consideration. One example of a global effort to mitigate the effects of greenhouse gases on the global climate is the Kyoto Protocol to the United Nations Framework Convention on Climate Change, which is an amendment to the international treaty on climate change, assigning mandatory targets (GHG targets) for the reduction of greenhouse gas emissions to signatory nations. The Kyoto Protocol includes flexible mechanisms which allow some economies to meet their GHG targets by purchasing GHG emission reductions (often called “carbon credits”) from elsewhere. These carbon credits can be bought or otherwise obtained either via financial exchanges (such as the new EU Emissions Trading Scheme) or from projects which reduce emissions in other economies.
Although several countries (most notably the United States) have not yet and may never ratify the Kyoto Protocol, there are also private initiatives in, for example, the United States where units of the government and private companies can voluntarily agree to reduce their GHG emissions. While joining the program is voluntary, members of this program have legally enforceable requirements for GHG reductions. Currently, this initiative is administered by the Chicago Climate Exchange (CCX). The CCX also hosts a trading exchange which facilitates the sale of carbon credits by members who do not release the amount of allowed GHG, and which facilitates the purchase of emission reductions (carbon credits) by members who are not able to achieve their required GHG reductions through their own operations. GHG reduction projects anywhere in the world are eligible for trading carbon credits on the CCX.